Many colour displays operate by combining a colour filter plate with an array of electronic shutters to give controllable selection of e.g. red, green and blue areas. The colour filter must be aligned or registered with the shutters, must allow through as much of the required colour of light as possible and as little as possible of the unwanted colours. Often the colours are separated by a black matrix, to preserve colour purity in the case of small misalignments, and in particular to shield light from thin film transistors (TFTs) if they are present.
A common arrangement of shutters is a rectangular array of rectangular pixels, though other more complex arrangements have been proposed. The array may be defined on one substrate by an active matrix circuit, where the other substrate has a common ground plane, or by the intersection of row electrodes on one substrate, and column electrodes on the other. In the first case, the colour filter/black matrix must be aligned in two dimensions. In the second case, the colours can be arranged in stripes aligned with the electrode pattern to simplify alignment along the stripe direction. The pixels are usually clustered in groups, typically of three (triads—Red Green and Blue to match the colour receptors of the human eye), making a square ‘superpixel’ which can display a range of colours, or black and white when viewed from a distance beyond which the eye can resolve the individual pixels. Other arrangements have been proposed, such as ‘quads’ of four subpixels—red, two greens and blue for example. These are more difficult to register, as they have to align in both the row and column direction; however they offer several benefits:                improved appearance of image edges when displayed—sub pixels are square not rectangular;        reduction in the pitch of interconnect in one direction (from 3× superpixel pitch to 2×);        possible reduction in driver cost from r+3c to 2r+2c (r=#rows*row driver cost);        small improvement in overall aperture (interpixel gap)2;        opportunity to improve the colour gamut of the display by adding a fourth colour to R, G and B.        
In practice the colour filter plate is expensive to manufacture, and the image quality is strongly affected by this component. Typically the patterns are made by a number of photolithographic steps. Inkjet or similar printing has also been proposed, wherein a series of ‘wells’ are made (usually photolithographically) which are then filled with colour filter material such as a dyed or pigmented resin. Here the wells have to be registered with the electrode structures.